Exemplary embodiments of the present invention relate to the art of combined cycle power plants and, more particularly, to a heat recovery steam generator for a combined cycle power plant.
Conventional combined cycle power plants employ a gas turbine system operatively coupled to a steam turbine system. The gas turbine system includes a compressor coupled to a gas turbine. The steam turbine system includes a high pressure (HP) turbine portion operatively coupled to an intermediate pressure (IP) turbine portion that, in turn, is coupled to low pressure (LP) turbine. Generally, the HP, IP and LP turbines are employed to drive a generator. In a typical combined cycle power plant, exhaust gas from the gas turbine is passed to a heat recovery steam generator (HRSG). The HRSG includes three different pressure heaters corresponding to three steam turbine pressures, e.g. HP, IP, and LP for a high performance combined cycle power plant. The HRSG also receives low energy steam from the HP steam turbine exhaust passing from the HP steam turbine. The low energy steam is used to reheat steam in the different pressure heaters for enhanced efficiency. The reheated steam is then passed back to power a lower pressure stage of the steam turbine.
Conventional HRSG systems employ finned pipes through which flow water and/or steam. The finned pipes are exposed to hot exhaust gases from the gas turbine. The hot exhaust gases flowing over the finned pipes raise a temperature of the water/steam to form high energy steam. The high energy steam is utilized to power the steam turbine to enhance combined cycle power plant efficiency. Flowing the water/steam through the finned pipes creates a significant pressure drop. The pressure drop creates design constraints that effect how much reheated steam can be introduced back into the steam turbine.